The truth about bypass protein

January 23, 2007 11:27 am

The long-awaited results of a study into the economics of strategic
protein supplementation of late pregnant and lactating sheep and
Angora goats have been released by agricultural researcher Jan Hoon of Grootfontein Agricultural Development Institute at Middelburg in the
Eastern Cape.

The long-awaited results of a study into the economics of strategic protein supplementation of late pregnant and lactating sheep and Angora goats have been released by agricultural researcher Jan Hoon of Grootfontein Agricultural Development Institute at Middelburg in the Eastern Cape. Roelof Bezuidenhout reports.

The study addressed many assumptions and misconceptions about protein supplementation, especially about high bypass and low bypass protein sources. Bypass protein, also known as rumen undegradable protein, is that part of the feed protein that’s not degraded in the rumen, but digested and absorbed in the small intestine. Good sources of high bypass protein include feedstuffs such as fishmeal and oilcake meals. These are, however, usually more expensive than feed sources with a low bypass protein content.

‘’Smallstock farmers now have enough information to plan their feed supplementation programmes, and at the same time save money by using less expensive rations or none at all, depending on conditions. Prevailing ­grazing conditions will have a large effect on how your animals react to supplementation,” says Jan Hoon of the Grootfontein Agricultural Development Institute. ”For example, more emphasis should always be placed on supplementing animals on grass veld than on shrub veld (bossieveld), especially during the dry season.’’

The research, conducted over a five-year period on farms in the southern Cape, Western Cape, Northern Cape, Free State, KwaZulu-Natal, Mpumalanga and Eastern Cape, showed that while supplementation of ewes during late pregnancy and lactation generally improved their body weight, the growth rate of lambs/kids and weaning percentages, the response was only worthwhile when grazing was relatively poor in quality or quantity. Under such conditions, for example on sour grassveld or stubble lands, high bypass protein diet had a positive effect – particularly on the number of lambs weaned per ewes mated. Differences in gross margin per ewe were mainly influenced by differences in the weaning percentages of the different groups.

The average cost of supplementary feeding for the control, low and high bypass groups were R0,00, R34,84 and R39,82 per ewe per year respectively.

General recommendations
According to Hoon, the type of grazing available in terms of quality and quantity is probably the main factor in determining whether supplementation is needed, and what type and how much supplementation should be fed. The prevailing grazing conditions – type, quantity and quality of ­vegetation – should dictate the type, period and amount of supplement needed to ensure that a supplementary programme during late pregnancy and lactation pays.

‘’As weaning percentage is so important in the economic viability of supplementation, the focus should be on the high producers in the flock, namely ewes with twins. Ultrasound scanning is a valuable management tool to identify ewes with multiple foetuses. Give more attention to these animals in a supplementation programme,’’ Hoon says.

He also suggests that farmers should evaluate the climatic conditions of individual years such as amount and distribution of rainfall, and the expected grazing conditions. ‘’The rainfall in the month before the ‘supplementation period’ will often determine whether or not supplements will be necessary, and if necessary, the type, amount and duration. Under favourable grazing conditions, the supplementation period can be shortened since the milk production of the ewes decline after six weeks into the lactation period, while lambs/kids also become less dependent on their mothers,” says Hoon.

‘’The price and the availability of different feeds are important factors when deciding on a supplement programme. The current price of different feeds can influence decision-making regarding whether or not to supplement, as well as the amount of supplement to be supplied. So, you can save money by matching the levels of bypass protein you feed to late pregnant and lactating ewes to the veld types and conditions,’’ Hoon suggests.

The results in various farming location
To include as much of the diverse vegetation found in the country’s smallstock areas, the project was carried out at 16 locations – 13 with sheep and three with Angora goats.

At the start of the project, at each ­location, a flock of the farmer’s ewes was mated as one group and randomly divided into three equal groups. The groups were then placed in different camps, comparable in size and veld quality and quantity, for the 12-week supplementation period. Where grazing conditions allowed, a control group was kept with no supplement, while the two treatment groups received supplements with a high and low rumen undegradable protein (UDP) content respectively. Two supplement diets were fed at 300g/animal/day for four weeks prior to lambing and 400g/­animal/day for eight weeks after lambing.

The nutritional value of all the diets used had the same protein (about 25% CP) and energy (55% to 60% TDN) content, with the only difference in the levels of bypass protein in the two treatment diets. The bypass protein contents of the low and high bypass diets were 2,8% to 3,3% and 5,5% respectively. As the project was repeated with the same nucleus of animals in each group, no significant carry-over effect with regard to increased reproduction rate due to the effect of supplementation during the previous lambing season was seen.

Between the two supplement groups (low and high bypass), differences in growth rate of lambs/kids were generally small, but it seems that protein supplementation had a positive effect on the milk production of ewes, compared to no supplementation, as is reflected in a higher growth rate of lambs/kids until 42-day age at most of the locations. The same tendency was observed for weaning weight of lambs/kids. But there were relatively small differences between the supplement groups.

Also, ewes receiving ­supplementation were better able to maintain body weight during lactation than ewes not ­receiving any supplement, depending on the grazing conditions. Between the two ­supplementation groups, the body weights of the ewes varied with some in favour of the high bypass and other in favour of the low bypass groups. But the differences in conception rate among the different groups on the farms were relatively small.

Sheep results
The gross margin/ewe was higher for the control group compared to the high bypass group on good-quality lucerne pastures (Heidelberg and Caledon), while no differences were observed between the two supplement groups on poorer-quality lucerne pastures (Heidelberg).

On wheat stubble (Malmesbury and Porterville), supplement of ewes with high bypass diets had an economic advantage over low bypass protein diets. On poor-quality Cynodon spp pastures (Caledon), the ewes receiving supplement had a higher gross income than the control group, especially supplementation with high bypass protein diets.

On Karoo shrub veld (Fraserburg) and mixed grass and shrub veld (Philippolis), the control groups receiving no supplementation had the highest gross margin/ewe, compared to the two supplement groups.

In the sour grassveld areas (Noupoort, Cedarville and Ermelo) the ewes receiving supplements with a high bypass protein content had a higher gross margin per ewe than ewes receiving low bypass diets.

Supplementing mutton sheep with low and high bypass protein diets at the two locations in the Northern Cape (Pofadder and Koopmansfontein) had no economic advantage, compared to ewes not receiving any supplements.

What about the Angoras?
It was only economically viable to supplement animals at one location (Willowmore), but not at the other two locations (Jansenville and Graaff Reinet). However, supplementation (low and high bypass) of Angora ewes during late pregnancy and lactation had a positive effect on consistency of fibre diameter along the length of the fibre.